Improvements in or relating to circuit interruption devices

摘要

A trip apparatus (10) for a circuit interruption device (12) comprises a coil (22) that is operatively connectable to a circuit interruption device (12). The coil (22) is configured to selectively operate the circuit interruption device (12) to interrupt a current flowing through the circuit interruption device (12) when the current exceeds a threshold. The trip apparatus (10) also includes a current measuring device (24) that is configured to selectively measure a coil current (I t ) flowing through the coil (22) to determine a measured coil current signal (26). In addition the trip apparatus (10) includes a monitoring device (28) which is configured to determine the derivative (30) of the measured coil current signal (26) and to perform a correlation of the derivative (30) of the measured coil current signal (26) and a reference derivative (42) of a reference coil current signal (44) to determine a correlation output. The monitoring device (28) is further configured to compare the correlation output with a reference correlation threshold to determine whether an operating condition of the coil (22) is normal or abnormal.